Cooperative and stimulated emission in poly(p-phenylene-vinylene) thin films and solutions

We discuss cooperative and stimulated emissions and separate their respective contributions to the emission spectral narrowing in thin films and solutions of poly($p$-phenylene-vinylene) derivatives. Whereas cooperative radiation is favored in films with poor optical confinement, directional stimulated emission is dominant in dilute solutions and thin films with superior optical confinement. Spectral narrowing in the latter case could be achieved by increasing either the excitation length or excitation intensity, from which we determined the optical gain and loss coefficients at the 0-1 emission band assuming a simple amplified spontaneous emission model. We found that the threshold excitation intensity for stimulated emission in neat films is mainly determined by self-absorption and that the gain saturates at emission intensities of about ${10}^7{\mathrm{W}/\mathrm{c}\mathrm{m}}^2.$